Enhanced plasmonic third-harmonic generation in graphene layers via Anderson localization induced by disordered gold gratings

We report the enhancement of third-harmonic generation (THG) in graphene layers in the mid-infrared frequency range through the introduction of structural disorder in plasmonic gold gratings. The structure consists of three stacked graphene sheets placed atop both periodic and disordered gold gratings on a SiO₂ substrate. The resonance frequency and THG efficiency can be tuned via electrostatic gating by adjusting the Fermi level. Introducing disorder by varying air gaps between gold elements breaks the translational symmetry, giving rise to highly localized plasmonic modes—a signature of Anderson localization. As disorder increases, transmittance changes and nonlinear enhancement becomes more pronounced. A 10% disorder nearly doubles the THG output (from 1.9 to 3.8 W), while the strongest field confinement occurs at 60%. This interplay between structural disorder, localized field enhancement, and graphene’s third-order nonlinearity enables tunable and efficient THG. The gold–graphene hybrid platform offers a promising route toward disorder-assisted nonlinear plasmonics within the range investigated in this work.